For conversion of fuel energy into heat, so-called impulse or high-speed burners are used. The fuel and the combustion air are mixed together and ignited in a high-heat resistant combustion chamber manufactured mostly out of ceramic material. The resulting hot combustion gas flows through a nozzle-shaped outlet with high speed in the heating space, which is formed either by the furnace room itself or by the inner space of a radiant tube. The outlet of the combustion chamber can be constricted in a nozzle-shaped manner or can be formed by a nozzle crown, wherein the axes of the nozzle openings are parallel to each other or are oriented so as to diverge from each other. The mechanical energy of the gas stream, which is being discharged from the combustion chamber and which partially originates from the fuel, serves to mix and circulate the gases in the heating room, which further assists the temperature equalization in the desired manner. Such a burner is for example described in DE 34 22 229 A1.
Furthermore, from EP 0 293 168 A2 an industrial burner is known that includes a high-heat resistant combustion chamber disposed outside of the furnace room. The fuel guiding device includes a primary fuel nozzle, which opens at a rear wall of the combustion chamber that opposes the combustion gas outlet, and a secondary, heat-insulated fuel nozzle extending through the combustion chamber, which secondary nozzle opens near the combustion gas outlet. This burner is operated according to a two-stage combustion, wherein less that 50% of the total fuel supplied to the burner is introduced via the primary fuel nozzle into the combustion chamber, which is continually supplied with the entire amount of the combustion air. This primary fuel is burned with a high air surplus by forming a long flame that reaches up to the mouth of the secondary fuel nozzle near the outlet of the combustion chamber. The combustion of the remaining fuel introduced via the secondary fuel nozzle takes place directly in the radiant tube with a low air surplus.
Similarly, a burner operable according a two-stage operation is known from EP 0 685 683 B1, in which two fuel outlets are provided in a combustion chamber separated from each other in the axial direction; the outlets are selectively supplied with fuel in a first and in a second combustion operation state. In particular, when starting up the burner, the fuel supply device, which discharges into the combustion chamber separated from the nozzle-shaped outlet of the combustion chamber in the furnace room, is used in order to introduce fuel into the combustion chamber and to enable combustion in the combustion chamber. In the second operation state, the other of the fuel outlets is solely utilized, which introduces the fuel immediately proximate to the combustion chamber outlet, so that unburned fuel adjacent to the air arrives at the furnace room unmixed with the combustion air. The mixing of the fuel and the combustion air then first takes place in the furnace room.
Starting therefrom, it is an object of the invention to provide an industrial burner that is simple to construct for low NOx-emissions and is flexible to operate, and a method for operating the industrial burner.